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Periodic Reporting for period 4 - FireBar-Concept (MULTI-CONCEPTUAL DESIGN OF FIRE BARRIER: A SYSTEMIC APPROACH)

Reporting period: 2020-07-01 to 2020-12-31

The development of science and technology provides the availability of sophisticated products but concurrently, increases the use of combustible materials, in particular organic materials. Those materials are easily flammable and must be flame retarded to make them safer. In case of fire, people must be protected by materials confining and stopping fire. It is one of the goals of the FireBar- Concept project to design materials and assembly of materials exhibiting low flammability, protecting substrates and limiting fire spread.

The objective of FireBar-Concept was to make a fire barrier formed at the right time, at the right location and reacting accordingly against thermal constraint (fire scenario). This fire barrier was developed in several ways according to the chemical nature of the material and/or of its formulation:

- Heat barrier formed by inherently flame retarded materials (e.g. mineral fibers, ceramic …) and exhibiting low thermal conductivity (note the assembly of those materials can also provide low thermal conductivity controlling porosity and its distribution)
- Evolution of reactive radicals poisoning the flame and forming a protective ‘umbrella’ avoiding the combustion of the material
- Additives promoting charring of the materials and forming an expanding carbonaceous protective coating or barrier (intumescence)
- Additives forming a physical barrier limiting mass transfer of the degradation products to the flame

The FireBar-Concept project is multidisciplinary and it involved expertise in material science, chemical engineering, chemistry, thermal science and physics. The approach was to make 5 actions linked together by transverse developments: (i) fundamentals of fire barrier, (ii) multi-material and combination of concepts, (iii) modeling and numerical simulation, (iv) design and development of experimental protocols and (v) optimization of the systems.

The main achievements of the FireBar-Concept project are: (i) the quantitative understanding of experimental conceptualized fire barrier and their numerical simulation, (ii) the combination of optimized multi-material structure containing fire retardant with low emissivity thin coating, (iii) multi-scale modeling and simulation using fractal theory and (iv) design of bench scale fire scenarios for mimicking extreme fire.
The project started working on the fundamentals of fire barrier and making virtual materials by numerical simulation. The goal was to define the governing parameters of a fire barrier. To support numerical simulation, an experimental bench was designed and built to make comparison between modeling and model material. Several model materials were evaluated including steel, ceramic block, polyisocyaranurate (PIR) foam and intumescent paint. Different numerical models were built considering the specific features of the materials (e.g. ablation at the surface of the materials or intumescing materials). The results show the models can capture the specific behavior of the materials such as the ablation of PIR foam upon radiative heating and the intumescence phenomenon. It was possible thanks to novel protocols measuring heat capacity, heat conductivity, thermal diffusivity and estimating kinetic values associated to the decomposition of the material. Those values were measured as a function of temperature of the decomposition degree of the material. Novel in-depth techniques to characterize gaseous and condensed phases of materials/residues issued from fire scenarios are also developing.

In addition to numerical simulation, an innovative small-scale bench was built mimicking different scenario based on jetfire. It is able to a large range of thermal constraints permitting to examine the response of fire barrier in different scenarios. New flame-retardants were also synthesized based on the concept of ‘thermal triggering’ making highly thermally stable structure upon heating.

Based on this knowledge and using additive manufacturing, multi-material structures containing fire retardant were made. An original bio-inspired design (honeycomb-like structure) was elaborated, 3D printed and optimized by the combination of numerous concepts (oxygen inhibitor system, physical barrier, low emissivity coating). Thanks to this association of design and concepts, the multi-material exposed to an external radiant heat flux of 50 kW/m² based on the ISO 13927 standard of the mass loss cone calorimeter shows a very low reaction to fire with a fast-self-flame extinguishment and an extremely low total of heat release rate (less than 10 kW/m²) evidencing its outstanding efficiency. In short, they exhibit extremely low flammability and lightweight offering a broad range of applications.
The project started on Jan 1, 2016 for a duration of 60 months. Our progress beyond the state of the art is:

(i) the development of novel protocols to measure thermophysical properties of decomposing materials and considering their anisotropic features (if any). It offers a way to characterize materials and to get accurate values to feed numerical models.
(ii) the development of fully instrumented bench-scale test designed to mimic different types of fire scenarios
(iii) new design of materials exhibiting extremely low flammability
(iv) Development and application of fractal theory for making multi-scale modeling
Organization of the FireBar-Concept projet
Temperature field of intumescent coating foam showing expansion (virtual material)
Graphical abstract of methodologies developed in the FireBar-Concept project